1. Field of the Invention
This invention relates to photographic cameras, and, more particularly, to an automatic exposure control system which is established by combination of a photographic exposure operation and control adapter unit with a camera. Still more particularly, it relates to an adapter unit which permits the selection of the exposure time preselection automatic daylight exposure range, exposure aperture preselection automatic daylight exposure range and automatic flash exposure range in which an exposure is made by the camera.
2. Description of the Prior Art
There are known two automatic exposure control methods, one of which is to control operation of the diaphragm mechanism in automatic response to preselection of an exposure time, namely the so-called "shutter preselection automatic exposure aperture control method" (hereinafter abbreviated as "shutter preselection type method"), and another method which is to control operation of the shutter mechanism in automatic response to preselection of an exposure aperture, namely, the so-called "diaphragm preselection automatic exposure time control method" (hereinafter abbreviated as "diaphragm preselection type method").
Of these two methods, the shutter preselection type method provides the advantage of permitting for the photographer to select a suitable exposure time based on this personal experience and insight so as to reduce the percentage of image-oscillation recorded photographs, but it provides the disadvantage that the exposure value representing an effective exposure aperture derived from the exposure operation and control device of the camera can not be observed prior to making an exposure by the photographer who is accordingly incapable of adjusting the depth of image field to a desired level.
On the other hand, the diaphragm preselection type method provides the advantage of permitting for the photographer to adjust the depth of image field as desired prior to making an exposure, but it has the disadvantage of increasing the percentage of image-oscillation recorded photographs taken particularly when dark objects are photographed with increased exposure times which can not be taken into account by the photographer prior to making an exposure. These two methods of automatic exposure control have both merits and demerits. In application to practical photography, therefore, proper selection of the shutter preselection and diaphragm preselection automatic exposure control ranges is required case by case to increase the percentage of photographs taken under such situation which will be found acceptable.
Most of the commercially available cameras are equipped with only one of these shutter preselection and diaphragm preselection automatic exposure control ranges, and moreover, the control devices therefor are generally incorporated in the camera bodies. With these type cameras, however, it is, of course, impossible for the camera equipped with the shutter preselection automatic exposure range to make an exposure in the diaphragm preselection automatic exposure range, and, conversely, it is of course impossible for the camera equipped with the diaphragm preselection automatic exposure range to make an exposure in the shutter preselection automatic exposure control range.
On the other hand, camera with adapter units detachably mounted thereon for assisting the camera in making an exposure either in the shutter preselection automatic exposure range or in the diaphragm preselection automatic exposure range have found relatively wide acceptance by the public. As far as is known, however, there has been developed no single adapter until now which when associated with a camera makes it possible for the camera to make an exposure by selection of the shutter preselection and diaphragm preselection automatic exposure ranges. Therefore, if the photographer desires to make an exposure by selection of these two automatic exposure ranges, he must be provided with two types of adapter units, one of which performs the shutter preselection mode and another type adapter unit which performs the diaphragm preselection mode. This will be very inconvenient for the photographer.
To solve the above mentioned problems arising from the provision for permitting selection of the shutter preselection and diaphragm preselection automatic exposure ranges made in the combination of the two types adapter units, a solution has been proposed, as for example, in U.S. Pat. No. 3,544,104 which discloses a camera equipped with these two automatic exposure ranges. In order to switch the camera between these two ranges, there is provided an aperture plate having an opening arranged in front of a photosensitive element and carrying both an operating member of a switch and a slider engaging a resistor. If the photographer desired to make an exposure in the shutter preselection automatic exposure range, the aperture plate is manually moved to set a pointer provided therein to a desired shutter speed, thereby the resistor is brought into connection with shutter control circuit through the above mentioned operating member, while the photosensitive element is brought into connection with an exposure meter circuit for automatically determining an effective exposure aperture. On the other hand, if an exposure in the diaphragm preselection automatic exposure range is desired, the aperture plate is manually moved to set the pointer to a desired diaphragm value, thereby the resistor is brought into connection with the exposure control circuit through the operating member, while the photosensitive element is brought into connection with the shutter control circuit for automatic control of the exposure time.
Such an automatic exposure control apparatus provided with the shutter preselection automatic exposure range and the diaphragm preselection automatic exposure control range is itself, however, relatively complicated in construction, and is increased in bulk and weight, thereby creating a large difficulty in incorporating the apparatus in a compact camera due to the limitation of the space available in the camera body without sacrificing the simplicity of the internal structure of the camera and the manageability thereof due to an increase in the bulk and weight of the camera body. Another disadvantage is to increase the production cost of the camera. Further, it is to be noted that such a camera necessarily permits only the automatic exposure control always in making an exposure but not the non-automatic exposure control in making an exposure with manual settings of both the shutter speed and the diaphragm value which is an important function of the camera, thereby giving an additional disadvantage of limiting the range of application of the camera to photography.